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Review of Blasting operations of Snsnmit Brick <br />Impacts & Controls for Blast Noise, 2.3 cont' <br />US 13M Air blast Limits VU 895, 1980) <br />Lower Frequency L.hnit of tMNwm tg System- aYsiftum LwsW <br />0.1 Hens hl8h Pan system Fist Response 134 Peak <br />2 Mertz hlgh pass system Flat Response 13- Peak <br />6 or 8 Mertz hlah pass system Flat Respomw 128 Peak <br />C- wel9hted system tar events with <br />dutstion tees than Z.0 see. Slow lteMmm 106 Peak <br />Figure 2.6--USBM Recommended Blasting Air Overpressure Limits <br />2.3.2 Air Overpressure I imitatiews <br />The regulatory limit defined by USBM, and promulgated by Colorado State Department <br />of Labor Regulations, for airblast measured with 2-Hz response seismographs is 133 dB-L. <br />As indicated in Figure 2.6, damage to old or poorly glazed windows does not occur until <br />overpressure reaches about 150 d&L More importantly, since the decibel scale is a <br />logarithmic ratio, the actual overpressure at 150 dB-L is 0.092 psi, versus 0.013 psi at 133 <br />dB-L. Therefore, the actual pressure at the 133-dB-L limit, is over seven times <br />(0.092/0.013) lower than the threshold damage level at 150-dBL The relationships <br />between actual overpressure expressed in psi and decibel scale measurements are shown in <br />the following forms of Equation 3. 1. <br />dB=20Logj0(P1Pd or P=10(0120) xPo (Equadon 3.1) <br />Where dB - demo, P ovapn=we (Psi), P, a Refimce pressure (29 x 10-9 past <br />Review of Blasting operations of Summit Brick <br />21